Tap changing furnace transformer



1965 G. A. WILSON, JR 3,204,176

TAP CHANGING FURNACE TRANSFORMER Filed April 26, 1961 3 Sheets-Sheet l \w) LA) \LAJ/ w INVENTOR. 60ra0n fl M'Lson J31 flttarng 1, 1965 G. A. WILSON, JR 3,204,176

TAP CHANGING FURNACE TRA1 ISI""ORIVIER Filed April 26, 1961 3 Sheets-Sheet 2 IN VEN TGR. Gem 0n y? MZson Jr? G. A. WILSON, JR 3,204,176

TAP CHANGING FURNACE TRANSFORMER 3 Sheets-Sheet 5 Filed April 26, 1961 Fig. 3

Aug. 31, 1965 IN VEN TOR. 60721077 fi Misc)? J BY flat/army United States Patent 3,204,176 TAP CHANGING FURNACE TRANSFORMER Gordon A. Wilson, Jr., Washington, Pa., assignor to McGraw-Edison Company, Milwaukee, Wis., 21 corporation of Delaware Filed Apr. 26, 1961, Ser. No. 105,625 8 Claims. (Cl. 323-43.5)

This invention relates to electrical power transformers and, more particularly, to furnace transformers having noload tap-changing equipment.

The ratio of transformation of electrical transformers is usually changed by increasing or decreasing the number of active turns in one transformer winding with respect to another winding. Adjustment of the voltage ratio between the transformer primary conventionally accomplished by providing one of the transformer windings with a plurality of taps connected to stationary contacts on a multiple position switch having a contact selectively movable into engagement with the stationary contacts to exclude or include a desired number of turns of the tapped Winding and thus vary the number of active turns in the winding.

High current stationary induction apparatus such as furnace transformers must supply heavy current at low voltage and be adjustable to deliver such current -at a large number of secondary voltage settings. The number of transformer voltage ratios required necessitates the provision of a large number of tap connections in each phase primary winding and means to change the tapped windings between delta and star connections. In a conventional furnace transformer taps are provided in the high voltage phase windings, the tap connections are brought to a terminal board within the transformer casing under the transformer oil, the terminal board is provided with an arrangement of studs and links to permit selection of the desired taps, and electrical connections are brought from the terminal board to a tap changer external of the casing to permit connecting the high voltage windings in star or delta and the selection of a limited number of voltage ratios. When such a furnace transformer is initially placed in service, the desired tap connections and voltage ratios to be available at the external tap changer are selected by properly positioning the links on the terminal board underneath the oil. The external tap changer permits connection of the windings in star or delta and the selection of such limited number of voltage ratios, but if after a period of operation of the furnace transformer a different voltage ratio is desired than that available at the external tap changer, it is necessary to de-energize the transformer and let it cool before the links on the terminal board can be changed. The terminal board is usually accessible through a manhole in the transformer casing cover, and it is necessary to unbolt each link separately under the oil and move it to a newly selected position when it is desired to select other voltage ratios. The operator must enter the transformer through the manhole and manually disconnect the links on the terminal board individually under the oil and reconnect them. It will be apparent that the furnace transformer is out of service for a considerable period of time while the transformer is cooling and the links are being changed on the terminal board.

It is an object of the invention to provide a furnace transformer wherein all of the possible voltage ratios can be selected externally of the transformer casing. It is a further object of the invention to provide a furnace transformer wherein it is unnecessary for an operator to enter the transformer and change links on a terminal board under the oil in order to select all the available voltage ratios. A still further object is to provide such an improved tap changer furnace transformer wherein it is unand secondary windings is 3,204,176 Patented Aug. 31, 1965 ice necessary to cool the transformer before changing taps and wherein the shut down time in which the transformer is out of service during the tap change is substantially reduced in comparison to prior art construction.

Another object of the invention is to provide -a novel indexing mechanism for furnace transformer tap changing equipment.

These and other objects and advantages of the invention will be better understood from the following detailed description when taken in conjunction with the accompanying drawing wherein:

FIG. 1 is a schematic circuit diagram of a preferred embodiment of three phase tap changer furnace transformer of the invention;

FIG. 2 is a section view taken along line 2-2 of FIG. 3 through the tap changing equipment associated with one phase of the furnace transformer of the invention;

. FIG. 3 is a partial front view of the tap changing equipment of the invention;

FIG. 4 is a front view taken along line 4-4 of FIG. 2 showing the novel indexing mechanism for the delta star switch, the supporting frame and bevel gears being removed to better illustrate the construction; and

FIGS. 5, 6 and 7 are partial views illustrating the operation of the indexing mechanism shown, in FIG. 4.

Referringto the drawings and the circuit diagram of FIG. 1 in particular, a three phase furnace transformer 10 has primary phase windings 11A, 11B, and 11C adapted to receive power from the line conductors A, B, C of a three phase electrical power system and permanently connected thereto by conductors 12A, 12B, and 12C respectively. The letters A, B and C are used as suffixes to reference numerals throughout the description to designate like elements associated with the three phases. Furnace transformer 10 is illustrated as having four low voltage winding sections Al-AZ associated with primary'phase winding 11A, four low voltage winding sections Bl-BZ associated with phase winding 11B, and four low voltage winding sections C1-C2 associated with primary phase winding 11C. The four low voltage winding sections associated with each phase may be connected in parallel to supply the required heavy current.

Tap changing equipment provided externally of the transformer casing to permit selection of any of the possible transformer voltage ratios bychanging tap connections and connecting the primary phase windings 11A,

11B, and 11C in delta or star includes a multiple position tap changing switch 14 and a delta-star switch 15 associated with each phase. has seven stationary contacts Each multiple position switch 14 1-7 arranged in a circle, and

16 connected by leads 17 to the seven stationary contacts 1-7. Each multiple positon tap changer. switch 14 is provided with a rotatable contact 18 movable sequentially into engagement with the stationary contacts 1-7.

Each delta-star switch 15 includes a pair of arcuate stationary contacts S and D arranged in a circle and a rotatable contact 20 adapted to engage the arcuate contacts S and D. The rotatable contact 18 of each multiple position switch 14 is electrically connected by a conductor 21 to the rotatable contact 20 of the associated delta star switch. The S stationary contacts of all three delta star switches 15 are commoned by leads 24.

Stationary contacts D of delta-star switches 15A, 15B .and 15C are connected by conductors 25, 26 and 27 to the phase windings 11B, 11C, and 11A respectively.

Means described hereinafter are provided to simultaneously index the multiple position switch movable contacts 18A, 18B, and 18C between stationary contacts 1-7, to simultaneously wipe delta-star switch movable contacts 20A, 20B, and 20C across one of the arcuate contacts S or D associated therewith and maintain continuous electrical engagement with said one arcuate contact While the contacts 18 are being indexed between tap positions 1-7, and to simultaneously actuate delta-star switch movable contacts 20A, 20B, and 20C between the arcuate contacts S and D when the multiple position switch movable contacts 18A, 18B and 18C are operated between predetermined tap positions, preferably when the multiple position switches are stepped between stationary contacts 1 and 7. When the movable contacts 20A, 20B, and 20C engage arcuate contacts S of the delta-star switches 15, the transformer primary phase windings 11A, 11B, and 11C are connected in star. Assuming the tap changing switch rotary contacts 18 are on stationary contacts 7 as shown in FIG. 1 and that movable cont-acts 20A, 20B, and 20C of the delta-star switches engage arcuate contacts S, a portion of the 'star connection may be traced through two windings beginning from power line conductor A, conductor 12A, primary winding 11A, a tap 16, a conductor 17, stationary contact 7A, movable contact 18A, conductor 21A, movable contact 20A, arcuate contact S of delta star switch 15A, conductor 24 which forms the neutral, arcuate contact S of switch 15B, movable contact B, conductor 21B, movable contact 18B, stationary contact 713, a conductor 17, a tap 16, winding 11B, and conductor 12B to power line conductor B.

Assuming the delta star switch movable contacts 20 engage arcuate contacts D and multiple position switch movable contacts 18 engage stationary contacts 7, as shown in FIG. 1, delta connection of the primary windings 11A, 11B, and 11C may be traced from power line conductor A, conductor 12A, primary winding 11A, 8. tap 16, a conductor 7, stationary contact 7A, movable contact 18A, conductor 21A, movable contact 20A of delta star switch 15A, arcuate contact D, conductor 25 to winding 11B and conductor 12B to power line conductor B, a tap 16 on winding 11B, a conductor 17, stationary contact 713, movable contact 18B, conductor 21B, movable contact 20B, arcuate contact D of delta star switch 15B, conductor 26 to primary phase winding 11C and conductor 12C to power line conductor C, a tap 16 on winding 110, a conductor 17, stationary contact 7C, movable contact 180, conductor 21C, movable contact 20C, arcuate contact D of delta-star switch 150, and conductor 27 to winding 11A and conductor 12A to power line conductor A.

Inasmuch as delta-star switch movable contacts 20 are in continuous electrical engagement with arcuate contacts S or arcuate contact D while multiple position switch movable contacts 18 are indexed into sequential engagement with stationary contacts 17, all fourteen of the possible transformer voltage ratios can be selected externally of the transformer casing.

Referring to FIGS. 2-7, a preferred embodiment of operating mechanism for the multiple position switches 14 and novel indexing mechanism for the delta-star switches 15 are illustrated. The multiple position switches 14 and delta-star switches 15 for all three phases are housed within a compartment on the sidewall of the transformer casing (not shown) having a rear insulating panel 30 through which conductor bolts from the tap changing equipment movable and stationary contacts extend into the oil-filled interior of the transformer casing to connect to conductors 17 (not shown) from the primary winding taps 16 and to conductors 21 and 24-27 (not shown). The multiple position switch 14 for each phase is disposed above the associated delta-star switch 15 for said phase. As illustrated in the drawing each multiple position switch 14 includes seven arcuately disposed stationary contacts 17. Each stationary contact 17 includes a metallic member 32 having a radially inward extending fiat blade portion 33 and being rigidly secured to a threaded metallic pin 34 extending through an aperture in insulating panel 30. Insulating collars 36 surround metallic pin 34 on opposite sides of panel 30, one collar 36 being disposed between panel 30 and stationary contact member 32. A not 38 threaded onto pin 34 on the side of the panel 30 within the transformer tank clamps the insulating collars 36 against opposed sides of panel 30 to fixedly mount stationary contact member 32 on panel 30. Conductors 17 (not shown) from the taps 16 on the associated primary winding 11 are connected to terminal pins 34 within the transformer tank.

Rotatable contact 18 of multiple position switch 14 includes a metallic collector ring member 40 disposed axially of the circle about which the stationary contact members 32 are arranged and rigidly secured to a threaded terminal pin 42 extending axially through an aperture in panel 30. Insulating collars 43 surround terminal pin 42 on opposite sides of panel 30, one collar 43 being disposed between panel 30 and collector ring member 40. A nut 44 threaded onto terminal pin 42 on the side of the panel 30 within the transformer casing cornpresses the collars 43 against opposite sides of panel 30 and fixedly mounts collector ring member 40 on panel 30. Conductor 21 (not shown) is connected to terminal pin 42 within the transformer tank.

Multiple position switch rotatable contact 18 is carried by a metallic rotating arm and includes a pair of 0pposed, radially extending, flat contact members 51 carrying button contacts 53 at the radially inner end thereof which bear against opposite sides of the collector ring member 40 and button contacts 54 at the radially outer end thereof which engage opposite faces of the blade portions 33 of the stationary contact members 32. The flat contact members 51 are bifurcated and fit over web portions 55 of rotating arm 50 disposed in a plane transverse to the plane of panel 30. (See FIG. 3.) Registering clearance apertures are provided in the flat contact members 51 and in a web portion 56 of the arm 50 in the plane of the blade portions 33 and disposed between the flat contact members 51. Headed pins 57 extend through the registering clearance apertures to mount the fiat contact members 51 on arm 50, and the heads on pins 57 bear against one fiat contact member 51. Springs 58 surrounding pins 57 and compressed between the other fiat contact member 51 and nuts 59 threadably engaging pins 57 resiliently bias the fiat contact members 51 toward each other and urge the contact buttons 53 into high pressure engagement with the collector ring member 40 and urge the contact buttons 54 into high pressure engagement with the blade portions 33 of the stationary contacts 32.

An axial compartment 62 in rotatable arm 50 receives an insulating shaft 63 having a plurality of circumferential skirts 64 to increase the length of creepage path along the axial length thereof. Axially extending pins 65 and 66 protrude into openings in opposite ends of insulating shaft 63. A through pin 67 secures axial pin 65, insulating shaft 63, and rotatable arm 50 together. Similarly, a through pin 68 rigidly secures axial pin 66, insulating shaft 63, and at Geneva gear 69 carried on shaft 63 together. Axial pin 65 is journalled within a bearing 70 disposed in an axial compartment in collector ring member 40 to rotatably support one end of shaft 63. Axial pin 66 is journalled within a bearing 73 disposed within an aperture in a vertical support panel 75 to rotatably support the other end of shaft 63.

A Geneva pinion crank arm 76 carried by a rotatable tub shaft 77 is adapted to engage and intermittently rotate Geneva gear 69 when stub shaft 77 is rotated. One revolution of stub shaft 77 actuates Geneva gear 69 to index multiple position switch movable contact 18 between adjacent stationary contact members 32. Stub shaft 77 is journalled within a bearing 79 disposed in gear afiixed to an upper horizontal operating shaft the multiple position switches 14A, 14B, and 14C of all three phases and carries three of said bevel gears 85 which engage the bevel gears 83 carried by the three stub shafts 77. It will be apparent that rotation of upper horizontal operating shaft 86 through 360 degrees will step each movable contact 18A, 18B, and 18C to the succeeding stationary contact and thus accomplish a tap change.

Each delta-star switch 15 includes two flat-spaced apart, arcuate, metallic stationary contacts S and D arranged in a circle. Arcuate contacts S and D are secured by bolts 90 to metallic support members 91 which are rigidly secured to threaded terminal pins 92 extending through apertures in insulating panel 30. Insulating collars 94 surround terminal pins 92 on opposite sides of panel 30, one insulating collar 94 being positioned between panel 30 and support member 91, and a nut 95 threadably engaging terminal pin 92 clamps the insulating collars 94 against opposite sides of panel 30 and rigidly mount-s arcuate contacts S and D on panel 30. Conductors 24, 25, 26, and 27 (not shown) are connected to terminal pins 92 within the transformer casing.

A metallic collector ring member 96 positioned axially of the arcuate contacts S and D and having a circumferential flange portion 97 in the plane of contacts S and D is rigidly secured to a threaded terminal pin 98 extending through an aperture in panel 30. Insulating collars 99 surround terminal pin 98 on opposite sides of panel 30, and a nut 101 threadably engaging terminal pin 98 clamps insulating collars 99 against opposite sides of panel 30 and rigidly mounts collector ring member 96 on panel 30.

Delta star switch rot-ary contact 20 includes two radially extending flat contact members 103 carried by a rotatable metallic arm 104 and having contact buttons 105 on the radially outer end thereof bearing against opposed sides of the arcuate contacts S and D and contact buttons 106 on the radially inner end thereof engaging opposite sides of the collector ring 97. Registering clearance apertures are provided in the flat contact members 103 and in a web portion 108 of the rotatable arm 104 in the plane of the arcuate contacts S and D and disposed between the fiat contact members 103. Headed pins 110 extend through the registering clearance apertures to mount the flat contact members 103 on rotatable arm 104, and the heads of the pins 110 bear against one fiat member 103. Springs 113 surrounding the pins 110 and compressed between the other flat contact member 103 and nuts 115 threadably engaging pins 110 resiliently urge flat contact members 103 toward each other and urge the contact buttons 106 into high pressure engagement with the collector ring 97 and urge the contact buttons 105 into high pressure engagement with opposed faces of the arcuate contacts S and D. The fiat contact members 103 are bifurcated and fit over web portions 116 of the rotatable arm 104 in a plane transverse to the plane of panel 30 (see FIG. 3).

An axial compartment 118 in rotatable arm 104 receives an insulating shaft 119 having a plurality of circumferential skirts 120 to increase the length of the creepage path in an axial direction. Axial pins 121 and 122 extend into openings in opposite ends of insulating shaft 119. A through pin 124 rigidly secures axial pin 121, shaft 119, and arm 104 together. Axial pin 121 is journalled within a bearing 126 within an aixal compartment in collector ring member 96 to rotatably support one end of shaft 119, An index gear 128 surrounds the other end of shaft 119, and a through pin 129 secures index gear 128,. shaft 119, and axial pin 122 together. Axial pin 122 is journalled within a bearing 130 within an aperture in support panel 75 to rotatably support the other end of shaft 119.

Index gear 128 has two circumferentially spaced apart v sets 131 and 132 of external teeth 133, and in the embodiment illustrated in the drawing each set 131 and 132 comprises fourteen teeth 133 with spaces therebetween where teeth are omitted. Index gear 128 also carries in the portions between the tooth sets 131 and 132 a pair of radially extending guideways 135 which are analogous to the slots in a Geneva gear.

A stub shaft is rotatably journalled within a bearing 141 disposed in registering apertures through vertical support panel 75 and a support casting 142 secured to support panel 75 by bolts 144. Stub shaft 140 carries a pinion 145 for driving index gear 128 and preferably having two driving pins 148 and 148 extending parallel to the axis of rotation of pinion 145 and disposed on opposite sides of such axis and adapted to engage and displace the teeth 133 on index gear 128 and thus rotate gear 128 when stub shaft 140 is rotated (see FIG. 4). One revolution of stub shaft 140 circumferentially displaces index gear 128 approximately the distance between two teeth 133, or approximately eighteen degrees, and thus also advances movable contact 20 approximately eighteen degrees along arcuate cont-act S or D. Arcuate contacts S and D each subtend approximately 150 degrees, and movable contact 20 is wiped across arcuate contact S or D and maintains continuous electrical contact therewith while stub shaft 140 makes seven revolutions and the driving pins 148 and 148' engage and advance each of the fourteen teeth 133 of a set 131 or 132.

Stub shaft 140 carries a bevel gear 150 which engages a bevel gear 151 carried by a lower horizontal operating shaft 152. Shaft 152 is a common driving shaft for all delta star switches 15A, 15B, and 15C and carries three of said bevel gears 151 which engage the bevel gears 150 carried on the stub shafts 140 of the delta star switches 15A, 15B, and 15C.

A veritcal drive shaft rotatably journalled in the support castings 80 and 142 is actuated by a reversible compound wound motor (not shown) of the furnace transformer tap changer control apparatus (not shown) and is rotated through one revolution whenever it is desired to change a tap and vary the voltage ratio of the transformer. Vertical shaft 160 carries two vertically spaced apart bevel gears 161 and 162. Upper bevel gear 161 engages a bevel gear 164 secured to the upper horizontal operating shaft 86 for indexing all three multiple position switches 14; lower bevel gear 162 engages a bevel gear 165 secured to the lower horizontal operating shaft 152 for all the delta star switches 15. Rotation of the compound motor (not shown) in the control circuit to actuate vertical drive shaft 160 through one revolution simultaneously rotates upper horizontal shaft 86 through 360 degrees to index the movable contact 18 of all three multiple position switches 15 between stationary contacts and also actuates lower horizontal shaft 152 through 360 degrees to displace two teeth 133 and advance index gear 128 and movable contact 20 of each delta star switch through approximately 18 degrees while maintaining movable contact 20 in continuous electrial engagement with arcuate contact S or D. r Pinion 145 is afiixed to a Geneva pinion, or crank arm, 166 carrying a crank arm pin 167 adapted to enter a slot formed by a guideway 135 and advance index gear 128 through a sufficient angle to disengage one set 131 or 132 of teeth 133 from the pinion driving pins 148 and to bring the other set of teeth 133 into engagement with the driving pins 148 and to simultaneously disengage delta star switch movable contact 20 from one arcuate contact S or D and to bring said movable contact 20 into engagement with the other arcuate contact S or D, thus changing the connection of the primary phase winding 11A, 11B, and 11C from star to delta, or vice versa. Crank arm pin 167 is rotated into slot 135 when the multiple position switch contacts 18 are indexed between predetermined tap positions.

In FIG. 4 the delta star switch movable contact 20 is shown in full lines at rest in engagement with arcuate contact D and driving pin 148 is in engagement with the teeth 133 of set 132. In FIG. stub shaft 140 and crank arm 166 have been rotated from the rest position of FIG. 4 through approximately 135 degrees to a position wherein crank arm pin 167 has entered a slot 135 on index gear 128 and the succeeding drive pin 148' has come into engagement with the last tooth 133 of set 132 and begun to displace said tooth circumferentially. FIG. 6 illustrates rotation of stub shaft 140 and crank arm 166 through an additional ninety degrees from FIG. 5 and shows that crank arm pin 167 has displaced index gear 128 from the position shown in FIGS. 4 and 5 to a position wherein tooth set 132 is disengaged from driving pin 148' and the tooth set 131 has come into engagement with driving pin 148. FIG. 7 illustrates the novel indexing mechanism after stub shaft 140 and crank arm 166 have been rotated through a complete revolution back to the rest position wherein tooth set 131 is now in engagement with driving pin 148, movable contact 20 has been disengaged from the full line position on arcuate contact D shown in FIG. 4 and moved to the dotted line position in engagement with arcuate contact S, and crank arm pin 167 is disengaged from index gear guideway 135.

Delta star switch movable contact 20 is actuated between arcuate contacts D and S whenever the multiple position switch 14 is stepped between predetermined tap positions, preferably when tap changer switch movable contact 18 is indexed between stationary contacts 1 and 7. It will be apparent that delta star switch movable contact 20 continuously engages and is advanced along an arcuate contact S or D to maintain the star, or delta, connection of the primary windings 11A, 11B, and 11C while the multiple position switch 14 is indexed through seven tap positions, and that between predetermined tap positions 1 and 7 the crank arm pin 167 enters a guideway 135 and steps index gear 128 and delta star switch movable contact 20 through approximately 50 degrees to disengage movable contact 20 from one arcuate contact S or D and engage it with the other arcuate contact, thus changing connections for the transformer primary windings 11A, 11B, and 110 between star and delta. It will be readily apparent that all fourteen possible voltage ratios can be selected by the disclosed tap changer apparatus located exteriorly of the transformer and that it is unnecessary to cool the furnace transformer to permit an operator to enter the transformer casing before tap connections can be changed, thus substantially decreasing the time that the transformer is out of'service when making a tap change in comparison to prior art construction and eliminating the danger of the operator dropping tools in the transformer windings and subsequently causing failure of the transformer.

While only a single embodiment of the invention has been illustrated and described, many modifications and variations thereof will be apparent to those skilled in the art, and consequently it is intended in the appended claims to cover all such modifications and variations which fall within the true spirit and scope of the invention.

I claim:

1. A three phase tap changer transformer having associated with each phase a multiple position switch, a deltastar switch, and a phase winding having a plurality of taps, drive means, said multiple position switch having a plurality of spaced apart stationary contacts arranged in a circle and connected to said taps, a rotary contact adapted to sequentially engage said stationary contacts, and a shaft carrying said rotary contact; means actuated by said drive means for intermittently actuating said shafts of all of said multiple position switches simultaneously to index said rotary contacts between said stationary contacts, said delta star switch having first and second arcuate stationary contacts arranged in a circle, a movable contact adapted to engage said arcuate contacts and to be wiped across one of said arcuate contacts in a series of steps while maintaining continuous electrical engagement therewith and being electrically connected to said rotary contact of the associated multiple position switch, an index gear having a pair of circumferentially spaced apart sets of teeth, a rotatable shaft carrying said delta-star switch movable cont-act and said index gear, a pinion adapted to engage said teeth on said index gear and rotate said gear to wipe said movable contact through one of said steps across one of said arcuate contacts each time said multiple position switch rotary contacts are indexed between stationary contacts, a crank arm, and an input shaft carrying said pinion and said crank arm; said input shafts of all three delta star switches being actuated simultaneously by said drive means and each said index gear carrying means cooperating with said crank arm when said multiple position switch rotary contacts are actuated by said drive means between predetermined stationary contacts to actuate said gear to disengage one of said sets of teeth from said pin-ion and said delta star switch movable contact from said first arcuate contact and to engage the other of said sets of teeth with said pinion and said delta star switch movable contact with the second arcuate contact, said first stationary contacts of all of said delta-star switches being commoned and said second stationary contact of each delta star switch being electrically connected to the tapped winding associated with another phase.

2. A three phase tap changing transformer having three phase windings provided with taps and a multiple position switch and a delta star switch associated with each phase and drive means for said switches, said multiple position switch having a plurality of spaced apart stationary contacts arranged in a circle and connected to said taps and a rotary contact adapted .to sequentially engage said stationary contacts, means operated by said drive means for intermittently indexing said rotary contacts of all three multiple position switches between said stationary contacts, said delta star switch having first and second arcuate stationary contacts and a movable contact electrically connected to said rotary contact and adapted to alternately engage said first and second contacts and to be wiped across each said arcuate contact in a series of steps while remaining in continuous electrical engagement therewith, said first arcuate contacts of all of said delta star switches being electrically commoned, said second arcuate contact of each delta star switch being connected to said winding associated with another phase, means operated by said drive means for simultaneously actuating said movable contacts of all three delta star switches and for indexing each said movable contact one step across one of said arcuate contacts each time said rotary con tacts are indexed to a succeeding stationary contact, whereby said movable contact engages a new point on said arcuate contact each time said multiple position switch is indexed and erosion of said arcuate contacts is minimized, and means operated by said drive means for simultaneously actuating said movable contacts of all three delta star switches between said first and second arcuate contacts once for each revolution of said rotary contacts and when said intermittent indexing means steps said rotary contacts of said multiple position switches between predetermined stationary contacts.

3. A three phase tap changing transformer in accordance with claim 2 wherein said means for simultaneously actuating said deltastar switch movable contacts includes in each delta st-ar switch an index gear coupled to said movable contact and having a pair of circumferentially spaced apart sets of teeth, a pinion adapted to engage said teeth and rotate said gear to wipe said movable contact in a series of steps across one of said delta star switch stationary contacts, a crank arm, a rotary shaft carrying said pinion and said crank arm and actuated by said drive means, and wherein said index gear carries means cooperating with said crank arm when said pinion engages predetermined teeth of said sets to actuate said index gear from a first position wherein one of said sets of teeth engage said pinion and said movable contact engages said first contact to a second position wherein the other of said sets of teeth engage said pinion and said movable contact engages said second contact, and wherein said rotary shaft actuates said pinion to advance said movable contact through one step across one of said delta star switch stationary contacts when said multiple position switch rotary contact is indexed to a succeeding stationary contact and said rotary shaft rot-ates said crank arm to actuate said gear bet-ween said first and second positions when said multiple position switch rotary contact is actuated between predetermined stationary contacts.

4. In combination with a three phase transformer having associated with each phase a delta star .switch and a multiple position tap changer switch, drive means, said multiple position switch having an input shaft operated by said drive means and a movable contact carried by said input shaft and said multiple position switch movable contact being adapted to step between tap positions in response to indexing of said input shaft, said delta-star switch including two arcuate stationary contacts arranged in a circle, a rotary contact connected electrically to said movable contact of said multiple position .svvitch and being adapted to engage said arcuate contacts and be stepped across one of said arcuate contacts in a series of steps while maintaining continuous electrical engagement therewith, an index gear having two circumferentially spaced apart sets of teeth, a driven shaft carrying said rotary contact and said index gear, a pinion having two driving pins extending parallel to the pinion axis and disposed away from said axis and adapted to engage said teeth on said index gear and rotate said gear to wipe said rotary contact through one of said steps across one of said arcuate contacts each time said movable contact of said multiple position switch is stepped between tap positions, a crank arm, and a rotatable shaft actuated by said driving means and carrying said pin-ion and said crank arm; said index gear having a pair of slots adapted to engage said crank arm and said rotatable shaft actuating said crank arm to engage one of said slots and rotate said index gear to disengage one set of said teeth from said driving pins and said rotary contact from one arcuate contact and to engage the other set of said teeth with said driving pins and said rotary contact with the other arcuate contact when said tap changer switch input shaft is actuated by said drive means to index said multiple position switch movable contact between predetermined tap positions.

5. An electrical switch comprising, in combination, a pair of spaced apart arcuate stationary contacts arranged in a circle, a movable contact adapted to alternately engage said arcuate contacts and be wiped across each of said arcuate contacts in a series of steps, an index gear having a pair of circumferentially spaced apart sets of teeth, a rotatable shatt carrying said movable contact and said index gear, an input shaft, a driving pinion affixed to said input shaft and adapted to engage said teeth on said index gear and rotate said index gear to wipe said movable contact in said series of steps across one of said arcuate contacts, :a crank arm afiixed to said input shaft, said index gear carrying means cooperating with said crank arm when said pinion engages predetermined teeth of said sets to actuate said index gear to disengage one said set of teeth from said pinion and to engage a succeeding set of teeth with said pinion, said movable contact being wiped across one of said arcuate contacts and maintaining continuous electrical contact therewith while said pinion is in engagement with said one set of teeth and being alternately actuated between said arcuate contacts when said crank arm actuates said index gear to disengage said one set of teeth from said pinion and to engage a succeeding set of teeth with said pinion.

6. An electrical switch in accordance with claim 5 wherein said index gear has a plurality of slots equal in number to said sets of teeth and said crank arm carries a crank pin disposed away from the axis of rotation of said crank arm adapted to enter one of said slots and actuate said gear to index said movable contact between said arcuate contacts.

7. In a three phase transformer having a multiple position tap changing switch and a delta-star switch associated with each phase, common drive means for said tap changing switches and said delta-star switches of all three phases, each said tap changing switch including a r plurality of stationary contacts arranged in an arc and a rotary contact adapted to sequentially engage said stationary contacts, each said delta-star switch including a pair of arcuate stationary contacts arranged in a circle, a movable contact electrically connected to said rotary contact and adapted to alternately engage said arcuate stationary contacts, an index gear having a plurality of circumferentially spaced apart sets of teeth, a rotatable shaft carrying said movable contact and said index gear, a driving pinion adapted to engage said teeth on said index gear and rotates said gear and said movable contact. said movable contact being wiped across one of said arcuate stationary contacts in a series of steps and maintaining continuous electrical engagement therewith while said pinion is in engagement with one of said sets of teeth, a crank arm, an input shaft carrying said pinion and operated by said common drive means to actuate said movable contact through one of said steps across one of said arcuate stationary contacts each time said multiple position switch rotary contact is actuated between tap positions, said input shaft also carrying said crank arm and said index gear carrying means cooperating with said crank arm when said tap changing multiple position switch rotary contact is actuated between predetermined tap positions by said common drive means to rotate said index gear from a first position wherein one of said sets of teeth engages said pinion and said movable contact engages one of said arcuate stationary contacts to a second position wherein said pinion is disengaged from said one set of teeth and engages a succeeding set of teeth and said movable contact is in engagement with a succeeding arcuate stationary contact.

8. In a three phase transformer in accordance with claim 7 wherein said crank arm carries a crank pin away from the axis of rotation of said input shaft and said index gear has a plurality of slots adapted to receive said crank pin to actuate said index gear between said first and second positions.

References Cited by the Examiner UNITED STATES PATENTS 719,198 1/03 Cyr 74-436 1,167,854 1/ 16 Taylor 74-436 2,480,589 8/49 McKenney 323-435 2,484,576 10/49 Minneci 323-435 2,693,573 11/54 Perkins 323-43.5 2,709,777 5/55 Willis et a1. 323-435 2,811,615 10/57 Stowell 200-153 2,868,032 1/59 Miller 74-436 2,870,647 1/59 Lauxen 74-436 2,887,897 5/59 Eisler 74-436 2,915,694 12/59 Bogert 323-435 3,066,208 11/62 Fannon et a1. 200-153 3,084,238 4/63 Baskerville 200-153 LLOYD MCCOLLUM, Primary Examiner.

MILTON O. HI RSHFIELD, Examiner. 

2. A THREE PHASE TAP CHANGING TRANSFORMER HAVING THREE PHASE WINDINGS PROVIDED WITH TAPS AND A MULTIPLE POSITION SWITCH AND A DELTA STAR SWITCH ASSOCIATED WITH EACH PHASE AND DRIVE MEANS FOR SAID SWITCHES, SAID MULTIPLE POSITION SWITCH HAVING A PLURALITY OF SPACED APART STATIONARY CONTACTS ARRANGED IN CIRCLE AND CONNECTED TO SAID TAPS AND A ROTARY CONTACT ADAPTED TO SEQUENTIALLY ENGAGE SAID STATIONARY CONTACTS, MEANS OPERATED BY SAID DRIVE MEANS FOR INTERMITTENTLY INDEXING SAID ROTARY CONTACTS OF ALL THREE MULTIPLE POSITION SWITCHES BETWEEN SAID STATIONARY CONTACTS, SAID DELTA STAR WHICH HAVING FIRST AND SECOND ARCUATE STATIONARY CONTACTS AND A MOVABLE CONTACT ELECTRICALLY CONNECTED TO SAID ROTARY CONTACT AND ADAPTED TO ALTERNATELY ENGAGE SAID FIRST AND SECOND CONTACTS AND TO BE WIPED ACROSS EACH SAID ARCUATE CONTACT IN A SERIES OF STEPS WHILE REMAINING IN CONTINUOUS ELECTRICAL ENGAGEMENT THEREWITH, SAID FIRST ARCUATE CONTACTS OF ALL OF SAID DELTA STAR SWITCHES BEING ELECTRICALLY COMMONED, SAID SECOND ARCUATE CONTACT OF EACH DELTA STAR SWITCH BEING CONNECTED TO SAID WINDING ASSOCIATED WITH ANOTHER PHASE, MEANS OPERATED BY SAID DRIVE MEANS FOR SIMULTANEOUSLY ACTUATING SAID MOVABLE CONTACTS OF ALL THREE DELTA STAR SWITCHES AND FOR INDEXING EACH SAID MOVABLE CONTRACT ONE STEP ACROSS ONE OF SAID ARCUATE CONTACTS EACH TIME SAID ROTARY CONTACTS ARE INDEXED TO A SUCCEEDING STATONARY CONTACT, WHEREBY SAID MOVABLE CONTACT ENGAGES A NEW POINT ON SAID ARCUATE CONTACT EACH TIME SAID MULTIPLE POSITION SWICH IS INDEXED AND EROSION OF SAID ARCUATE CONTACTS IS MINIMIZED, AND MEANS OPERATED BY SAID DRIVE MEANS FOR SIMULTANEOUSLY ACTUATING SAID MOVABLE CONTACTS OF ALL THREE DELTA STAR SWITCHES BETWEEN SAID FIRST AND SECOND ARCUATE CONTACTS ONCE FOR EACH REVOLUTION OF SAID ROTARY CONTACTS AND WHEN SAID INTERMITTENT INDEXING MEANS STEPS SAID ROTARY CONTACTS OF SAID MULTIPLE POSITION SWITCHES BETWEEN PREDETERMINED STATIONARY CONTACTS. 